Filtration



May. 29, 1945. -w. KIERSTED. JR

FILTRATION 2 Sheets-Sfieet 1 Original Filed June 28, 1941 TwE WYNKDOP ZIEZSTED 12.. f A INVENTOR ATTO NEY I May 29, 1945.

R J D E T R E K w FILTRATION Original Filed June 28 1941 2 Sheets-Sheet 2 VIYNKO P UEEETED J2.

Sta A ATTORNEY Reisaued May 29, 1945' FILTRATION Wynkoop Kiersted, In, Scarsdale, N. Y., assignor, by memo assignments, to The Texas Company, New York, N. Y., a corporation of Delaware Original No. 2,348,822, dated May .18, 1944, Serial No. 400,208, June 28, 1941.

Application for reissue March 1, 1945, Serial No. 580,403

Claims.

This invention relates tofiltration and particularly to the separation 01' solids from a mix- Ezre of solids and liquid by continuous filtra- The invention broadly contemplates a continuous filter operation, uch as conducted with a continuous rotary filter apparatus, wherein the interior of the filter element bearing the filter cake is purged of mother liquor after the filter cake has emerged from the mixture undergoing filtration and has been subjected to a primary application of wash liquid, but prior to subjectins the filter cake to further application of wash liquiu in situ.

A continuous rotary filter'useiul in practicing the invention may comprise a hollow, rotating cylinder or comprise hollow rotating leaves with means for either creating vacuum within the interior or the filter element or for exerting positive pressure upon the exterior thereof.

A rotary drumfilter comprises a cylindrical filtering surface. The filtering surface in turn comprises a plurality of separate, segmental compartments or sections. Each compartment or section is connected by drain pipes to a conventional filter valve.

In operation, the rotating cylinder is partially submerged in the filtering mixture, the submergence being about 40 to 60% of the filtering surface. Solids are deposited on the submerged exterior portion of the filter surface to form a filter cake while liquid flows through the cake and through the filter surface into the interior of the submerged filter compartment from which it is discharged through the drain pipes into the filter valve and from there conducted to a filtrate receiver as primary filtrate.

As the cylinder rotatesthe filter surface with cake deposited upon it emerges from the filtermg mixture. Upon emerging from the filtering mixture, filtration continues coupled with washing of the filtercake so that mother liquor contained in the filter cake is displaced by the wash liquid and is draw into the interior of the filter compartment, from which it "is discharged through the drain pipes and filter valve into suitable filtrat receivers. Washing of the exposed filter cake'is effected with a wash liquid or solvent which is usually applied to the exterior of the exposed cake in the form of a spray.

After passage through the washing zone, the filter cake is subjected to drying by the passage through it of gas. Thereafter the cake is removed from the filter surface usually by applymg a slight reverse pressure toithe interior of the of the filter element.

filter element'causlng distension of the fabric and consequent loosening of the cake. Complete removal of the cake is eflected by a suitable defiector blade located adjacent to the exterior surface of the filter fabric. V

In large scale filter installations where the filter drum may have a diameter of about 8 to 10 feet the interior of each segmental section or compartment of the filter including the drain pipes connecting each section with the filter valve will comprise a substantial volume, for example, about 1 cubic foot. Consequently, as each section emerges from the filtering mixture the interior will be substantially filled with mother liquor its path ,of travel, 7

As already pointed out it is customary to apply a spray of wash liquid or solvent over the filter cake after it has emerged from the filtering mixture. In the usual operation, wash liquid is applied to the exterior of the filter cake immediately as it emerges from the filtering mixture for the purpose of effecting a piston displacement of mother liquor from the cake into the interior Upon continued rotation of the filter additional wash liquid isapplied to the exterior of the filter cake for the purpose of removing remaining mother liquor retained in the cake. Heretofore, the filter valve has been arranged so that filtrate produced durin the primary application of wash liquid to the exterior of, the ter cake is permitted to flow into the mother lquor filtrate receiver, and filtrate produced during the secondaryor continued ap- Dllc'ation of wash liquid is diverted through a separate discharge conduit toa separate receiver "as secondary or wash filtrate;

.vide for positive displacement of substantially However, this secondary filtrate usually contains a large amount of mother liquor, largely due to the fact that the mother liquor and primary wash liquid does not drain rapidly enough from the interior of the filter element and the drain pipes communicating with the filter valve.

One object of the present invention is to proall of the mother liquor from the 'emergent filt'er compartment immediately afterrthe primary ap-- plication of the wash solvent or wash liquid, This Figure 2 is a sectional view taken along the axis of the filter drum showing the interior of a portion of the filter drum and thefilter valve.

As shown in the figures the filter comprises a bowl I into which the mixture to be filtered is introduced througha pipe 2.

Within the bowl is a horizontal drum 3 rotatably supported by. a trunnion I. The trunnion terminates in the customary filter valve illustrated in the figures.

The cylindrical surface of the drum 3 is surrounded by a filter fabric in the conventional manner; The cylindrical portion of the drum is divided into a plurality of separate segmental sections X about 30 in number. Each Of these segmental sections is connected by leading and trailing drain pipes Y and Z respectively to the filter valve on the trunnion 4.

In operation of the filter, filtrate including mother liquor, wash solvent and mixture of mother liquor and wash solvent is drawn through the filter surface into each segmental section and .from there through the drain pipesv Y and Z to the filter valve from' which it is discharged through pipes I, 8 and 9 as will be described in more detail.

The solids are deposited in the form of a filter cake on the outer surface of the filter fabric while the main stream of mother liquor filtrate is dis charged through'pipe I. As the drum rotates the filter cake emerges from the filtering mixture, the

surface of which may be maintained at a point corresponding to that shown by the numeral I 0.

Upon emergence, the filter'cake is subjected to washing-by a spray ll of primary wash" liquid introduced through a spray extending through V the filter shell II. This wash liquid is forced through the cake to displace the mother liquor contained in the cake and thence into the interior of the filter section-to form filtrate relatively rich in mother liquor which is discharged through Y pipe 8, and is usually merged with the main stream of filtrate discharging through pipe I. After the filter cake passes zenith in its path 7 of travel it is subjected to a secondary application of wash liquid through spray IS, the filtrate produced in this zone being discharged through pipe 9.

Upon further rotation, the filter cake is subiected to drying by the passage through itof flue gas or other inert gas, such gas being supplied to the interior of the filter shell by a pipe not shown. Following this the filter cake is discharged. This isaccomplished by introducing a reverse pressure to the interior of the filter surface by means of gas introduced through a blowback pipe l5. In this way the filter fabric is distended and the cake removed therefrom by means of a knife or scraper ii. The dislodged cake is discharged into a trough ll of a conveyor.

Referring to Figure l and considering the operation of a vacuum filter-,it, will be seen that as soon as any section X has becomecompletely submerged, drain pipes Y and Z connectingthe tamed through the cake in the respective Zones. For example. it may be advantageous to maintain a lower pressure differential through the cake in the zone between blocks A and B than in the zone between block B and C, in order to prevent building too thick a cake during submergence of the segment. In other words, less vacuum is exerted within the segmentduring rotation through the zone between blocks A and B. A greater vacuum in the zone between blocks 13 and C prevents the cake slipping from the drum surface after emergence from the liquid leveL' Block B has awidth on the inner side equal to slightly more than the diameter of the port corresponding to pipe Z so that immediately after side of the section by way of pipe Z. As the section emerges from the liquid level the port corresponding to pipe Y connected with the leading edge of the section emerges into the'vacuum zone between blocks B and C.

The drainage of mother liquor continues until i block C (or alternately block C is reached.

Thus, assuming that the block is in the position of block C located at a point just before zenith, the port corresponding to pipe Y passes under block C and opens to a port within this block through which is supplied flue gas under about ipounds gauge pressure from; a pipe II.

The flue gas then flows through the pipe Y to section X, across the interior of the section and out through the trailing drain pipe Z.

The port openings and pipe sizes are advantageously proportioned to afl'ord several complete changes of flue gas through the section and piping while the port of pipe Yis opened to the port in block C in order to purge out all liquid. Block C may have an undercut channel or throttling groove, not shown, so that flue gas may be admitted to pipe Y at a gradually increasing rate engages the.

Where the'blockis in the position of C located just after the section passes zenith the purge gas is admitted through pipe Z instead of pipe Y and the liquid is purged out through pipe Y since pipe Y is on the lower side of the section after passing the zenith. After passing block C or alternately C, the section. travels to a position such as K. At this point the port corresponding to pipe Z passes under block A and at position X is opened to a port in the block A through which is supplied flue gas under pressure as in the case of block C The flue gas flows through the pipe Z and pur'ges liquid out through pipe Y to. the section between blocks C and A. This latter purging operation is for the purpose of preventthat a different pressure differential-may be main} '75 ing loss of wash liquid frornthe filter section X by blowback during cake discharge, at which time the port corresponding to pipe Y is open through block A to a supply otfiue gas under pressure.

Thus, by'providing the blocks C or O in the filter valve and introducing a purge gas through the ports therein as above described, the mother liquor is substantially entirely displaced and drained from the emergent filter sections prior to the secondary application of the wash liquid. and the mother liquor is substantially entirely removed as primary liltratethrough the pipes I and 8. The secondary wash liquid is substantially wash filtrate through the pipe lean in mother liquor.

The advantage of this arrangement is demon and is relatively strated in the case of filtering decolorizing clay from a mixture or clay and oil or from a mix-- ture of clay and color removal solvent such as described in my pending application, Serial No. 312,667, filed January 6, 1940, for Method of and apparatus for recovering adsorbent materials. Thus, operating in the conventional manner with: Y out the purging step, 1003 gallons per hour 01 filtrate are drawn oil from the' space between blocks C and A (in the direction of drum rota? tion) and 2063 gallons are drawn oil as combined liquid from the spaces between blocks A and C. On the other hand, when operating with purging step the respective volumes of liquid drawn oil are 364 and 2'782gallons per hour. In.

other words, with the'purging step some639 gal-l ions of filtrate, consisting mainly of mother liquor are diverted into primary filtrate that would otherwise be dischargedas secondary filtrate.

Thus, by means of the purging step of this invention washing of the filter cake to displace and remove retained mother liquor is rendered more eil'ective. The secondary filtrate obtained following the purging tepcontains a relatively small amount of mother liquor and, therefore, can be recycled in a conventional filtering operation as a diluent for the initial feed mixture to the filter. Where the purging step is omitted, the secondary filtrate is richer in oil and instead of recycling it it is necessary to subject it to a fractional distillation in order to separate the, wash liquid from the mother liquor.

However. where the purging step is practised, it is unnecessary to subject the secondary filtrate to the recovery operation thereby materially reducing the cost of the filtering operation. In

fact, the resulting reduction in cost is sufiicient to actually permit the application oi a larger volume oi wash liquid in the secondary washing step and thereby permit subjecting the filter cake to additional washing.

Numeral 19 in Figure 2 designates the rotating bearingsurface of the filter valve adjacent the end of the trunnion 4 and in which surface terminate the drain pipes X and Y, afiording communication with the aforementioned-segmental sections X of the filter surface. Numeral 20. designates a channel in the filter valve into which the blocks A, B and C -or C" are rigidly attached to the filter valve. These blocks are removable and are so formed as to provide a snug lit and l thus completely block the channel 20 at the point of their location. I I

As already described the trunnion l rotates with the filter drum, while the filter valve remains sta tionary. Therefore. since the blocks A. B and r? are rigidly attached -to-the filter valve'they slide over the movirfg surface I! of the trunnion I. The surface 1! is advantageously of brass while the blocks are tormedof steel and in this way-a slidable, substantially leakproof joint is provi ed between the trunnion land the blocks of it is contemplated that the, positiorrof the filter blocks relative to each other and to the filter valve channel may be adjusted depending upon the particular type of filtering operation being practised.

While application of the invention to the illtration of decolorizing clay from a mixture of such' clay'and liquid has been described, nevertheless it is contemplated the invention is applicable to varioupfiltering operations including, for exsimple, a dewaxing operation in which solidified wax is filtered from a chilled mixture of wax bearing oil and diluent or solvent liquid'.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations pended claims.

lclaim:

1. In the continuous filtration of solids from a mixture of solids and mother liquor by means comprising a plurality of hollow segmental filter elements whose leading and trailing portions are in fluid communication through separate drain pipes with a filter valve, the steps comprising rotating the drum so that each filter element sub merges within and then emerges from the mix ture, forming a filter cake of solids upon the exterior oi each element and forcing mother liquor through the cake into the interior of each charging mother liquor from the interior of an element through the filter valve as filtrate, sub- .iectin each-cakebearing element during continued rotation after emerging from the mixture and before reaching the zenith in its path of travel to a primary application of wash liquid to displace mother liquor from the cake into the inferior of the element. discharging displaced liquor through the filter valve,' i njecting ga through a. leading drain pipe interior of each partially washed cake-bearing element as it 2113- injection of said gas through said leadin drain pipe of each cake-bearing element as it moves awav f om said zenith. thereafter subjecting each partially washed cake-bearing element to a secondary application of wash liquid which is forced throu h the filter cake into the interior of th element to form secondary filtrate con istin mainly of wash liquid. and separately dischar ins s i secondarv filtrate liquid from the inteso rim f the filter element throu h the filt r valve 2. In the continuous filtration of solids from a mixture of solids and mother liquor by means of a continuous rotary drum filter, the filter drum I comprising a plurality of hollow segmental filter eiements whose leading and trailing portions are in fiuid communication" through separate drain pipes with afilter valve, the steps comprisin rotating the drum so that each filter element subj merges within and then emerges from the mixterior of each element and forcing mother liquor through the cake into the interior of each element during rotation through the mixture, discharging'mother liquor from the interior of an element through the filter valve as filtrate, subjecting each cake-bearing'element during continued rotation after emerging from the mixture and before reaching the zenith in its path of travel to a primary application of wash liquid to terior of the element, discharging displaced liquor through the filter-valve, injecting gas through a leading drain pipe to the interior of each partially washed cake-bearing element as it ap- 15 preaches said zenith, discharging the so injected should be imposed as are indicated in the apof a continuous rotary drum filter, the filter drum element during rotation through the mixture, disture, forming a filter cake of solids upon the exdisplace mother liquor from the cake into the in- I ondary application of wash liquid which is forced through the filter cake into the interior of the element to iorm secondary filtrate consisting mainly of wash liquid, separately discharging said secondary filtrate liquid from the interior of the filter element through the filter valve, rotating each 'cakesbearing element after said secondary washing through a drying zone, forcing gas through said cake during passage through the drying zone, then rotating each dried cakebearing element through a zone of cake discharge, and removing the cake therefrom during passage through saidcake discharge zone.

3. In the continuous filtration. of solids from .a mixture of solids and mother liquor by means 01' a continuous rotary drum filter, the filter drum comprising a plurality or hollow segmental filter elements'whose leading and trailing edges are in fiuid communication through separate drain pipes with a filter valve, the steps comprising rotating the drum so that each filter element submerges within and then emerges from the mixture, forming a filter cake of solids upon the exterior of each element and forcing mother liquor through the cake into the interior of each element during rotation through the mixture, discharging mother liquor irom the interior oian element through the filter valve as primary filtrate,subjecting each cake-bearing element during-continued rotation alter emerging from the mixture and before reaching the zenith in its path 01' travel to an application of wash liquid to displace mother liquor from the cake into the interior of the element, discharging displaced liquor through the filter valve, admitting gas to the interior of each element through its leading edge as it approaches said zenith after partial washing with said wash liquid, discharging so injected gas together with liquid consisting mainly of mother liquor irom the interior of said element through its trailing edge, discontinuing the admission of said gas through said leading edge after passing zenith, thereafter subjecting the partially washed cake-bearing element to turther washing with wash liquid which is forced through the filter cake into the interior of the element to iormsecondary filtrate consisting mainly of wash liquid, and separately discharging said secondary filtrate from the interior of the element through the filter valve.

4. In the continuous'filtration of .solids from a mixture of solids and mother liquor by means of a continuous rotary drum filter, the filter drum comprising a plurality oi' hollow segmental filter elements whose leading and trailing portions are in fluid communication through separate drain pipes with a filter valve, the steps comprising rotating the drum so that each filter element submerges within and then emerges from the mixture, forming a filter cake of solids upon the exterior of each element and forcing mother liquor through the cake into the interior of each element during rotation through the mixture, discharging mother liquor irom'the interior of an element through the filter valve as primary filtrate, subjecting each cake-bearing element during continued rotation after emerging from the mixture to an application of wash liquid to displace mother liquor from the cake into the interior of said element, discharging displaced liquor through the filter valve, admitting gas through a drain pipe to the interior of said element after partial washing with said wash liquid, said gas. being admitted thru a drain pipe nearest zenith in the path of travel of said element, discharging so admitted gas together with liquid consisting mainly of mother liquor from the interior of said element through a drain pipe farthest from zenith, discontinuing the admission of said gas vthrough said drain pipe nearest zenith after said element has moved a substantial distance in its path of travel, thereafter subjecting the partially washed cake-bearing element to further washing with wash liquid which is forced through the filter cake into the interior of the element to form secondary filtrate consistin mainly of wash liquid, and separately discharging said secondary filtrate from the interior of q the element through the filter valve.

' 5. In the continuous filtration of solids from a mixture of solids and mother liquor by means of a continuous rotary drum filter, the filter drum comprising a plurality of hollow segmental filter elements whose leading and trailing edges are in fluid communication through separate drain pipes with a filter valve, the steps comprising rotating the drum so that each filter ele-' ment submerges within and then emerges from the mixture, forming a filter cake of solids upon the exterior of each element and forcing mother liquor through the cake into the interior of each element during rotation through the mixture, discharging mother liquor from the interior of an element through the filter valve as primary filtrate, subjecting each cake-bearing element during continued rotation after emerging from the mixture to an application of wash liquid to displace mother liquor from .the cake into the interior of said element, discharging displaced liquor through the filter valve, after partial washing of each cake-bearingv element withsaid wash liquid admitting gas to the interior of said element through the edge thereof nearest the zenith in the path of travel of said element, discharging so admitted gas together with liquid consisting mainly of mother liquor from the interior or said element through the opposite edge thereof farthest from zenith, discontinuing theadmission of said gas through said edge nearest zenith after said element has moved a substantial distance in its path of travel, thereafter subjecting the partially washed cake-bearing element to further washing with wash liquid which is forced through the filter cake into the interior oi the element to form secondary filtrate consisting mainly oi wash liquid and separately discharg- 'ing said secondary filtrate from the interior of the element through the filter valve.

.- WYNKQOP KIERSTED, JR. 

